1. Field of the Invention
The invention is based on a gas probe for determining the concentration or temperature of a gas such as the exhaust gas components of an internal combustion engine.
2. Description of the Prior Art
One gas probe of the type with which this invention is concerned is known, for instance from European Patent Disclosure EP 0506897 B1, for use in exhaust gas analysis for internal combustion engines. Such gas probes have a metal housing, in which an elongated, planar sensor element is disposed, electrically insulated, with one region on the measurement side and one region on the connection side. In the connection region, the sensor element has contact faces, which are electrically connected to a measurement point located in the measurement region. The gas probe also has a contacting device, which contains conductor elements that are in conductive contact with the contact faces of the sensor element and which extend out of the housing. By means of a spring element that engages contact holder, the conductor elements are pressed onto the contact faces. The regions of the contact holder that contact the conductor elements are embodied in flat form.
One such gas probe is known, for instance from European Patent Disclosure EP 0506897 B1, for use in exhaust gas analysis for internal combustion engines. Such gas probes have a metal housing, in which an elongated, planar sensor element is disposed, electrically insulated, with one region on the measurement side and one region on the connection side. In the connection region, the sensor element has contact faces, which are electrically connected to a measurement point located in the measurement region. The gas probe also has a contacting device, which contains conductor elements that are in conductive contact with the contact faces of the sensor element and which extend out of the housing. By means of a spring element that engages a contact holder, the conductor elements are pressed onto the contact faces. The regions of the contact holder that contact the conductor elements are embodied in flat form.
Such gas probes serve to measure the temperature or determine the concentration of gas components in exhaust gases of internal combustion engines. To that end, the gas probe is secured in a measurement opening of an exhaust gas line of an internal combustion engine. The exhaust gas can reach temperatures of more than 1000xc2x0 C. in the exhaust gas line, and thus the gas probe is severely heated, and temperatures up to 800xc2x0 C. occur in the region of the contacting device. At such high temperatures, the conductor elements can become deformed by creeping processes. As a result, the deflection of the spring element out of its position of repose and thus the contact pressure can be decreased, and the contact of the conductor elements with the contact faces can be impaired or even disrupted entirely.
From European Patent Disclosure EP 0 087 626 B1, a gas probe with a clamp contact means is also known, with which means conductor elements bent into a U shape are put into contact, by means of a contact holder, with contact faces of a planar sensor element. The contact holder has a slot for receiving the sensor element. Through holes are also made in the contact holder, as well as indentations laterally on the slot. The indentations serve to receive one leg of the conductor element bent into a U, so that the conductor element and the sensor element are fixed by the contact holder and put into conductive contact. The other leg of the conductor element is disposed in one of the through holes. A spring element for nonpositive connection of the conductor element to the contact face of the sensor element is not provided in this clamp contacting means.
The gas probe of the invention has the advantage over the prior art that deformation of the conductor element from creeping processes can be largely prevented, even at high temperatures, for instance in the range of 800xc2x0 C., so that impairment of the contacting of the sensor element is precluded.
Because the conductor element is disposed in an indentation in the contact holder and is in contact with the contact face only by a region that protrudes from the indentation in the contact holder, it is attained that deformation of at least the part of the conductor element located in the indentation in the contact holder is reduced or even prevented entirely. Thus the contact pressure exerted by the spring element is at least largely maintained even at high temperatures, and thus adequate contact of the conductor element and contact face of the sensor element is assured.
Creeping is averted especially reliably if the conductor element protrudes by less than half its cross-sectional area from the indentation in the contact holder. Because the majority of the conductor element is located in the indentation, only the smaller part, protruding out of the indentation, of the conductor element can be subject to deformation, thus minimizing the loss of contact pressure from creeping of the conductor element.
Because the part of the conductor element located in the indentation makes up more than half the indentation in cross section, it is attained that the loss of initial tension from the deformation of the conductor element in the indentation that occurs in operation at high temperatures is only slight. The loss in initial tension is moreover calculable, since at most the conductor element can creep only until the indentation is entirely filled. Thus the loss of initial tension can be compensated for by the provision of a spring element, which has a correspondingly higher initial tension before the deformation of the conductor element occurs in the indentation.
If the conductor element is disposed by positive engagement in the indentation, deformation of the conductor element in the indentation is prevented entirely.
Because a high-temperature-resistant material is provided for the conductor element, the tendency to deformation at high temperatures is reduced.